Statics and dynamics of multivalley charge density waves in Sb(111)

Abstract

Charge density waves (CDWs), periodic modulations of the charge density, are among the most abundant and non-trivial ordered phases in condensed matter. Here we demonstrate the occurrence of multi-valley charge density waves (MV-CDW) on the semimetal Sb(111), a phenomenon previously observed at semiconductor surface inversion layers. The topological nature of the pocket surface states in Sb(111) ensures perfect nesting conditions giving rise to sharp peaks in helium atom scattering (HAS) diffraction spectra. The peculiar temperature dependence permits to distinctly associate the diffraction peaks with surface electron and hole-pocket states due to the non-trivial surface electronic band structure known from recent experimental data and present ab-initio calculations. Inelastic HAS spectra, besides providing the surface phonon dispersion curves in agreement with density functional perturbation theory calculations, reveal two additional dispersion curves of elementary excitations in the gap well below Rayleigh waves. They are attributed to collective excitations of the quasi-commensurate MV-CDWs associated with the surface electron M-pocket states at the Fermi level. These findings suggest that HAS can be regarded as a choice spectroscopy for the investigation of surface electronic excitations in the THz domain, opening up a new window for the search of collective phases at surfaces.

Helium–Surface Interaction and Electronic Corrugation of Bi2Se3(111)

“…Moreover, there appear to be features with increased intensity next to the first-order diffraction peaks (see, e.g., the top panel in Figure ). Additional features in diffraction scans due to spin-conserving electronic interpocket transitions have been observed for the semimetal Sb(111), and the observability of similar transitions in the TI Sb 2 Te 3 has been suggested by theory . The observation of additional dispersion curves in Bi 2 Se 3 in analogy to Sb(111) suggests a similar assignment of the additional peaks in the diffraction spectra.…”

Measuring the Electron–Phonon Interaction in Two-Dimensional Superconductors with He-Atom Scattering

“…The high sensitivity and resolution of HAS permit detection of CDWs where other conventional surface probes fail, and measurement of the dispersion curves of their collective excitations [14,16,19]. The additional possibility to directly estimate the e-ph interaction makes HAS an excellent tool to investigate superconducting (SC) layered chalcogenides.…”

Evidence for a spin acoustic surface plasmon from inelastic atom scattering

“… spin-echo (3HeSE) spectrometry, in particular, with its unprecedented resolution in the neV range, can in principle measure the ASP dispersion in the GHz domain. Recent HAS experiments have provided the dispersion curves of other THz electronic collective excitations such as phasons and amplitons occurring in charge density wave systems 60 , 61 and, with HeSE, in the long-period reconstructed surface 62 . As shown in the case of (111), bound-state resonance enhancement can be exploited in HAS experiments to amplify the response of low-energy electronic collective excitations 61 .…”